1. Field of the Invention
This invention relates to a transmission mechanism which comprises a traveling transmission system and a PTO transmission system and used for a working vehicle, such as a tractor, and more particularly to a transmission mechanism which is provided in the traveling transmission system with an auxiliary transmission having at least two transmission stages, such as a forward and rearward movement switching and a high-low speed switching, and in the PTO transmission system with a hydraulic PTO clutch and a PTO brake for braking a PTO shaft following disengagement of PTO clutch.
2. Description of Related Art
A conventional transmission mechanism for a working vehicle, such as a tractor, has a traveling transmission system having both a multi-stage transmission device and a PTO system transmission mechanism. In other words, a common input shaft transmits the power from an engine output shaft and is used to drive both the traveling transmission system and the PTO transmission system by using gears and the like. Conventionally, however, the traveling system transmission shaft and the PTO system transmission shaft are disposed in parallel to each other so that the separate spaces for transmission shafts of traveling and PTO systems are required to be axially disposed. In a case that the traveling system transmission device is the multistage transmission device, the disposing space thereof needs to be a considerably larger in part, whereby the transmission mechanism provided with both the traveling and PTO systems, the transmission shafts requires a further larger disposing space to that extent, and a housing for containing therein the mechanism must be of a large size.
Also, such the transmission mechanism for the working vehicle like the tractor is provided with both the traveling system and PTO system having the multistage speed change device, is well-known to be provided between the engine and the multistage speed change device with an auxiliary speed change device provided with at least two speed-change stages. For example, a transmission mechanism disclosed in the Japanese Patent Publication No. Hei 5-26686 or the Japanese Patent Laid-Open No. Hei 7-117507 is provided between the engine and the main multistage speed change device for the changing the speed of driving wheels with the speed change device for forward and rearward movement switching and for high-low speed changing.
The conventional traveling transmission mechanism is complicated in construction of assembling the main multistage speed change device, forward and rearward movement switching device and auxiliary high-low speed change device, in the same chamber, on the same shaft or on each shaft to be engageable with each other. For example, even when only the multistage speed changing device is intended to be applied with the maintenance work, both the multistage speed change device and auxiliary speed change device must be detached so that it is difficult that the auxiliary speed change device is detachably mounted.
In a case that such the auxiliary speed change device comprises a hydraulic clutch, supply structure for operating oil is complicated so that it is difficult to construct the hydraulic clutch to be easily detachably mountable. For example, the hydraulic clutch disclosed in the Japanese Patent Laid-Open No. Hei 6-297971 (in which the clutch is for PTO power change over), a valve for supplying the operating oil is built in a housing and a hydraulic oil pipe is interposed between the valve and the hydraulic clutch, whereby the piping must be removed when the hydraulic clutch is detached or mounted.
Meanwhile, such a conventional transmission mechanism for the working vehicle, which is provided with a PTO clutch of multistage plates and of hydraulic operation system and a brake mechanism for preventing inertial rotation are juxtaposed in the downstream side, is disclosed in, for example, the Japanese Patent Laid-Open No. Hei 6-297971, in which the brake mechanism is so constructed that braked members assembled integrally with the PTO clutch piston come into press contact with one disc-like braking member freely fitted onto the transmission shaft in the downstream side of PTO clutch, so as to brake the downstream side transmission shaft; the PTO system transmission shaft (or the PTO shaft itself). Also, the braking members are freely fitted on the PTO system transmission shaft, but is admitted to be idle in a predetermined angle (rotation reversely to the driving direction), because when the PTO shaft does not operate at all during the disengagement of PTO clutch, the PTO shaft at the working vehicle side and the transmission mechanism at the working machine side are not well connected.
The conventional PTO transmission system has the brake mechanism which brings one disc-like braked member in press contact with one disc-like braking mechanism, so that, when in comparison with the multiple disc system, an impact increases and the durability deteriorates. The braking mechanism is freely fitted onto the shaft at the downstream side of PTO clutch and the braked members are built in the clutch piston, whereby the braked members and braking members of the brake mechanism must be separated. Furthermore, an operation quantity of the braked member is restricted to the stroke of the clutch piston, the stroke must be adjusted every assembly so as to take much time. The idling allowable mechanism in the predetermined angle of the PTO brake is complicated in processing at a wall portion of transmission casing and expensive to produce.